1. Field of the Invention
The present invention relates, in general, to organic gate insulating films and organic thin film transistors using the same. More specifically, the present invention is directed to an organic gate insulating film, capable of increasing the electrical characteristics of a transistor when used, and an organic thin film transistor having the insulating film.
2. Description of the Related Art
Ever since the development of polyacetylene, a conjugated organic polymer that exhibits semiconductor characteristics, there has been vigorous research on an organic semiconductor including polymer as semiconductor materials, which became one of novel electronic devices with many application in a variety of fields, such as functional electronic devices and optical devices. This is because, when used in the organic semiconductor, organic polymers show many advantages of having various synthetic routes, being easily formed into fiber- or film-shapes, showing excellent flexibility and good conductivity, being manufactured at lower costs, and so on.
As one of many devices prepared by using the organic conductive polymers, an organic thin film transistor (OTFT) characterized by using the organic polymer as an active film has been studied since the 1980s. In recent years, a lot of research on such an OTFT has been done all over the world. The OTFT is similar in a structure to the conventional Si-TFT, but it is different in a sense of using the organic polymer as a semiconductor material instead of Silicon. In the process of the OTFT, thin film of semiconductor layer can be fabricated by printing-process under atmospheric pressure, not by plasma-using chemical vapor deposition (CVD) which is very troublesome but essential for the formation of a Silicon thin film and, furthermore, a roll to roll process using a plastic substrate can be used so it is possible to manufacture a more inexpensive transistor.
At present, the organic thin film transistor has been applied for drive devices of active displays and plastic chips of smart cards or inventory tags. In the organic thin film transistor, its performance that is normally evaluated by field-effect mobility, flashing ratio and threshold voltage has been enhanced to be close to that of α-Si TFT. In addition, such performance of the organic thin film transistor depends on various factors, including a degree of crystallization of the organic active film, charge characteristics at the interface between a substrate and the organic active film, carrier injection capability of an interface between a source/drain electrode and the organic active film, etc. In this regard, a variety of methods have been proposed to improve its performance. In particular, with the aim of decreasing the threshold voltage, U.S. Pat. No. 5,946,551 disclosed a method of using dielectric materials having a high dielectric constant (i.e. High-K materials) for example ferroelectric insulating materials such as BaxSr1-xTiO3 (BST), Ta2O5, Y2O3, or TiO2, and inorganic insulating materials, such as PbZrxTi1-xO3 (PZT), Bi4Ti3O12, BaMgF4, SrBi2(Ta1-xNbx)2O9, Ba(Zr1-xTix)O3 (BZT) , BaTiO3 or SrTiO3. For the organic thin film transistor, a silicon oxide film and an inorganic insulating material can be used as the gate insulating film. But, when the inorganic oxide material being used, the OTFT has no advantage in terms of processing, compared with the conventional TFT using silicon as semiconductor materials.
Meanwhile, the organic insulating film used in the prior art is composed of polyimide, benzocyclobutene or photoacryl. However, such an organic insulating film has been found to be inferior to inorganic insulating films in light of transistor characteristics (U.S. Pat. No. 6,232,157). Thus, in order for an organic thin film transistor to be used practically, organic insulating materials that are suitable for a printing process and can contribute to good transistor characteristics when used in OTFT should be urgently developed.